The reign of Queen Elizabeth I was a golden age for England. It was also a period when the country was the coveted goal – and bull’s-eye — in the Wars of Religion that plagued Europe.

The religious passions stirred up by Henry VIII’s break with the Roman Catholic Church and creation of his own Protestant brand was what was behind the growth of espionage in England.

In 1517, a monk, Martin Luther, started the Reformation by nailing his thesis against papal indulgencies to the front door of All Saints’ Church in Wittenberg, Germany. It led to a schism in Christianity between the Roman Catholic Church and those who broke from its teachings to form the Protestant Church. England swayed back and forth religiously. Under Henry and his short-lived heir Edward VI, it was Protestant. His daughter, Mary, a devoted Catholic, took it back to the Church of Rome.

Then came Elizabeth.

“As early in Elizabeth’s reign as the 1570s some exiles pressed the Pope and the King of Spain for a crusade against England and the forcible removal from power of Elizabeth and her government,” Alford writes. English emigres wrote plans for invasion and worked with foreign powers to topple Elizabeth’s government.

Alford, who taught at the University of Cambridge, has researched sixteenth-century archives, condensing his findings into a coherent and well-written narrative that is entertaining and readable. He keeps track of a vast number of characters, carefully explains the deadly plots and doesn’t get bogged down in boring minutia.

The most dangerous question of all was what to do with Mary Queen of Scots, a prisoner of Elizabeth’s, and the aim of the many Catholics to be placed on the throne of England.

Walsingham knew firsthand the dangers of religious conflict. He was the English ambassador to France in 1572 when the Catholic populace slaughtered Protestants by the thousands during the St. Bartholomew’s Day massacre in Paris. It scarred him so much that he wanted Mary dead, seeing her as the center of the Catholic plots. In the end, he won. Mary was tried and executed on Elizabeth’s reluctant orders.

A spy’s lot often ended with a traitor’s death of hanging, drawn and quartered. Alford shows the cost to those who spied for Walsingham and his successors.

There’s a danger of relying on the goodwill of princes after your usefulness is ended.

—“The Watchers: A secret history of the reign of Elizabeth 1,” by Stephen Alford; Bloomsbury Press, New York (400 pages, $35)